Reduction in functional antibody activity against Streptococcus pneumoniaein vaccinated elderly individuals highly correlates with decreased IgG antibody avidity

The pneumococcal polysaccharide vaccine is recommended as a means of preven ting invasive disease in the elderly. We compared responses to the 23-valen t polysaccharide vaccine in 46 previously unvaccinated, healthy, institutio nalized elderly persons (mean age, 85.5 years) with those in 12 healthy you nger adults (mean age, 37 years) by measuring prevaccination and postvaccin ation serum IgG antibody concentrations (by ELISA), functional antibody act ivity (by opsonophagocytosis), IgG antibody avidity, and passive protection in mice. Postvaccination IgG antibody concentrations for two serotypes (6B and 19F) of the five studied (4, 6B, 14, 19F, and 23F) were significantly lower in elderly than in younger adults; however, opsonophagocytic activity was significantly reduced for all serotypes in the elderly. Sera with redu ced opsonophagocytic activity (titer, <64) correlated with low IgG antibody avidity and protected mice poorly against pneumococcal challenge. In elder ly persons receiving polysaccharide vaccination, there was a significant re duction in the functionality of postvaccination antibodies, and this appear ed to increase with advanced age.